1. Field of the Invention
The present invention relates to a thermal processing apparatus irradiating a semiconductor wafer or a glass substrate (hereinafter simply referred to as “substrate”) with light thereby thermally processing the substrate.
2. Description of the Background Art
In general, a thermal processing apparatus such as a lamp annealing apparatus using a halogen lamp is employed in an ion activation step for an ion-implanted semiconductor wafer. This thermal processing apparatus heats (anneals) the semiconductor wafer to a temperature of about 1000° C. to 1100° C., for example, thereby activating the ions implanted into the semiconductor wafer. This thermal processing apparatus utilizes energy of light emitted from the halogen lamp thereby increasing the temperature of the substrate at a rate of about hundreds of degrees per second. The thermal processing apparatus utilizing such photoirradiation may monitor deterioration of the lamp with a photosensor.
However, it has been proved that the profile of the ions implanted into the semiconductor wafer is rounded, i.e., the ions are diffused by heat when the ion activation step for the semiconductor wafer is carried out with the thermal processing apparatus increasing the temperature of the substrate at the rate of about hundreds of degrees per second. When such a phenomenon takes place, the implanted ions are diffused even if the same are implanted into the surface of the semiconductor wafer in high concentration, and hence the ions must disadvantageously be implanted beyond necessity.
In order to solve the aforementioned problem, there has been proposed a technique of irradiating the surface of a semiconductor wafer with flash light through xenon flash lamps or the like thereby increasing the temperature of only the surface of the ion-implanted semiconductor wafer in an extremely short time (not more than several ms.). When the surface of the semiconductor wafer is heated through the xenon flash lamps in an extremely short time, only ion activation can be executed without rounding the profile of ions implanted into the semiconductor wafer due to an insufficient time for diffusion of the ions.
If a lamp unit having a plurality of such xenon flash lamps is not at all managed, however, deterioration of none of the xenon flash lamps can be detected in the lamp system as a whole but it follows that processing of the semiconductor wafer is continued while the quantity of light is reduced immediately under the deteriorated lamp. Consequently, it follows that semiconductor wafers partially causing processing abnormality in the surfaces thereof are disadvantageously produced in a large quantity.
Therefore, it is important to mange the xenon flash lamps to ameliorate or prevent the aforementioned drawbacks of the prior art. Presently there has been no concept of control in relation to the xenon flash lamps emitting flash light by instantaneously discharging energy of capacitors storing charges. Lamp management itself has been extremely difficult.
Indirect management by periodically sampling and inspecting processed wafers has generally been frequently employed as a method of managing xenon flash lamps. More specifically, whether proper thermal processing has been performed is inspected by taking out about one processed wafer per several lots and measuring the sheet resistance of the surface thereof. Even if an abnormality is recognized as a result of the inspection of this method, there is a high possibility that a large number of semiconductor wafers processed between the inspections suffer from processing abnormalities. Thus, this method is risky.
There has also been proposed a method of monitoring current characteristics in flash light irradiation thereby detecting abnormality of flash lamps. However, factors for deterioration of flash lamps include various ones such as blacking of glass tubes resulting from sputtering of electrodes, and it is impossible to detect such deterioration of flash lamps resulting from such a phenomenon by monitoring current characteristics.